1. Field of the Invention
The present invention relates to Bourdon pressure gauges. More specifically, it relates to a Bourdon pressure gauge having a direct-coupled electronic and visual readout.
2. Description of the Prior Art
Conventional Bourdon tube pressure gauges typically use a rotating pointer to provide visual readout. Generally, a Bourdon tube is positioned in an arcuate configuration with one fixed end in communication with a source of pressure to be measured and the other end free to move in response to flexing of the tube as caused by changes in such pressure. These gauges are provided with a pressure dial; and suitable linkage is included for connecting the free end of the Bourdon tube for indicating the changes in pressure sensed by the tube. Typically, the linkages and the length of the pointer provide a circumferential displacement of the pointer tip which is considerably amplified in comparison with the displacement of the tube end. By varying the tube design, gauges may be specifically constructed for measuring pressures ranging from 0 to 15 p.s.i. or for measuring pressures ranging from 0 to as high as 20,000 p.s.i. The main structural features of a rotating pointer Bourdon tube pressure gauge are illustrated in U.S. Pat. No. 3,504,548, issued to E. H. Grauel.
Similar gauges have been devised for providing an electrical readout. See, for example, U.S. Pat. No. 2,956,251, issued to E. J. Groeppinger et al., and U.S. Pat. No. 3,411,362, issued to J. Arasim, Jr. These gauges, in substance, use a rotating pointer to contact a variable resistor. In both cases, the displacements of the pointer ends which effect the contact are relatively large compared to the displacements of the tube. An alternative electrical readout gauge is described in U.S. Pat. No. 2,934,729, issued to M. E. Bourns. In this gauge, the free end of the Bourdon tube is directly connected to a contact with the variable resistor.
One of the major difficulties with electrical readout gauges is the fact that the addition of relatively complex circuitry between the mechanical sensing element and the readout introduces an additional source of error not readily perceived by the user. Circuits containing semiconductor devices such as transistors can produce an output which varies as a function of temperature or which gradually varies as a function of time. In remote sensors, even the length of the transmission line between the circuitry and its remote indicator may be a source of error.
These errors are not readily perceived because they arise in the circuitry rather than in the simple mechanical structure of the gauge. Electrical readout gauges do not typically have visual readout indicators against which the electrical readout can be checked, and the structures of such gauges are not readily adapted for providing, simultaneously, electronic and visual readouts that are directly coupled and of comparable accuracy. In general, such gauges have been designed to utilize the relatively small displacements as are required to confine the contact to regions of uniform resistivity. These displacements are too small to provide meaningful visual readouts.